Mozilla developer Bobby Holley discovered that it was possible to bypass some protections in Chrome Object Wrappers (COW) and Same Origin Wrappers (SOW), making them mutable by web content. This could be to used gain access to chrome privileged functions that are normally web inaccessible, leading to arbitrary code execution.
In general these flaws cannot be exploited through email in the Thunderbird and SeaMonkey products because scripting is disabled, but are potentially a risk in browser or browser-like contexts in those products.
Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Bobby Holley as the original reporter.
This issue does not affect the version of firefox and thunderbird as shipped with Red Hat Enterprise Linux 5 and 6